CAN’T Madonna afford to buy some gym equipment for her apartment? The privacy-obsessed pop star is ruffling feathers at the posh Upper West Side Reebok Sports Club, where, according to an insider, members were furious after club staff “closed off a row of six treadmills” in anticipa tion of her arrival. The tipster added that those working out in group exercise rooms are even forced to sweat in “black ened-out rooms,” making “two floors of the gym look like a prison with shuttered gates” so that nobody can catch a glimpse of her Madgesty.